1. Field of the Invention
This invention relates to a liquid crystal display device employing thin film transistors ("TFTs"), used as a switch matrix, and more particularly to a liquid crystal display device adapted to be driven with digital video data.
2. Description of the Prior Art
Recently, there has been used a signal transfer system changing of an analog image signal into a digital image signal feasible to the compression of information, in order to provide the high resolution picture with a viewer. A liquid crystal display panel has been developed that may be driven with the digital image signal instead of the existing analog image signal.
An digital-type liquid crystal display apparatus based on this development, as shown in FIG. 1, comprises a gate driver 12 for driving gate lines GL of a liquid crystal display panel, and a number of data driver integrated circuit, hereinafter referred simply to as "ID-IC", for time-divisionally driving data lines DL of the liquid crystal display panel 10. In the liquid crystal display panel 10, the TFTs, although not shown, are located at in intersections of the gate lines GL with the data lines DL, and liquid crystal cells are connected to each of these TFTs. The gate driver 12 drives the gate lines GL sequentially for the horizontal scanning interval every frame period through a gate control signal. In other words, the gate driver 12 sequentially drives the TFTs included in the liquid crystal panel 10 for every one line. Further, the D-ICs 14 convert video data into analog data signals every horizontal scanning interval using a data control signal and applies the converted analog video signal to the data lines DL. Specifically, each of the D-ICs 14 input video data corresponding to its input lines and converts the input video data into analog video signals. Also, each of the D-ICs 14 supplies the analog video signals to the data lines DL connected to the output line thereof. Accordingly, liquid crystal cells for a single line connected to the TFTs for that line control the light transmissivity in accordance with a voltage level of that line.
In the digital-type liquid crystal display apparatus having a configuration described above, since the D-ICs 14 drive the data lines corresponding to their output terminal, it has a disadvantage in that a great number of D-ICs are required, and that, hence, the circuit configuration and volume becomes large.
In order to overcome such a disadvantage in the conventional digital-type liquid crystal display apparatus, there has been suggested a liquid crystal display apparatus using time division demultiplexing. Examples of this liquid crystal display apparatus of time division system include one disclosed, in an article published in the 1993 edition of the IEEE Journal, titled "An LCD Addressed by a-Si:H TFTs with Peripheral poly-Si TFT Circuit" by Tanaka et al., and an article published, through "Euro Display '96", titled "Ar.sup.+ Laser Annealed Poly-Si TFT for Large Area LCDs" by Kato et al. According to these articles, the time divisional liquid crystal display apparatus improves the ON/OFF speed of TFTs by forming the TFTs to have a dual layer of a polycrystalline Si and an amorphous Si. Further, the time divisional liquid crystal display apparatus allows date lines to be time-divisionally driven by inserting a demultiplexer between output terminals of each of D-ICs and the data lines. According, the time divisional liquid crystal display apparatus could reduce a required amount of D-ICs into below half.
In the time divisional liquid crystal display apparatus, however, since the demultiplexer switches the data lines, the distance between data lines driven with a single demultiplexer becomes large. This causes a complication in the wiring arrangement of the liquid crystal display panel as well as a distortion of video signal. Also, since D-ICs have to sample video data for one line sequentially, sampling clocks with a frequency corresponding to the number of video data for one line should be supplied to the D-ICs.